Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

529
FXUS63 KLOT 151734
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1134 AM CST Mon Dec 15 2025

.KEY MESSAGES...

- Gusty southwest winds this morning will result in blowing and
  drifting snow with slippery travel conditions for open areas
  primarily south of a Streator to Kankakee to Rensselaer line.

- Moderating temperatures are expected through Thursday.

- Period of rain showers are expected late Wednesday night into
  Thursday, followed by blustery conditions and briefly colder
  conditions Thursday night and Friday.

&&

.DISCUSSION...
Issued at 254 AM CST Mon Dec 15 2025

Through Tuesday:

A strong high pressure ridge extending northward into southern
Illinois is quickly shifting southeast early this morning as a
decaying surface trough approaches the far northern Great Lakes.
A 50+ knot LLJ over Wisconsin is beginning to shift southeast
toward northern Illinois per recent KLOT/KMKX/KDVN VWP data. A
recent ACARS profile indicates that a very stout inversion (10C
increase between 500-2000ft) is present over the area. Because
of this, surface gusts have been quite sporadic so far. The very
strong stability will continue to be a limiting factor with
winds for at least the next few hours as the core of the LLJ is
lagging to the northwest. Meanwhile, abundant mid to upper-level
cloud cover over northern Illinois will continue to spread
southeast through the morning hours. While the overall low-level
gradient flow would support gusts to at least 20-25 mph through
the morning hours, minimal mixing through the morning hours
indicates that stronger winds within the inversion layer will
struggle to mix down to the surface. Still see the potential for
a window of gusts to 30 mph mid to late morning before the LLJ
slides southeast this afternoon, but those gusts may be more
sporadic in nature. Even with the delayed stronger winds, a
fluffy snow pack still remains primed for blowing and drifting
snow for open roads primarily around and south of a Streator to
Kankakee to Rensselaer line this morning.

A weakness in the low-level gradient extending northwestward
across the area tonight will result in light to locally calm
winds late this evening into the overnight hours. Thicker
mid/upper-level cloud cover will also diminish during this time.
With modest low-level moisture advection into the area from the
southwest later today below the remaining strong inversion,
conditions are prime for at least some patchy shallow fog to
develop across northern Illinois west of the Chicago metro.
Coverage and depth of any fog remains less clear given the
marginal and very shallow moisture profile, so have limited
forecast wording to only patchy at this time.

Increasing southwest winds under mostly sunny to partly cloudy
skies on Tuesday will boost temps to at least freezing for much
of the area. Deeper snowpack upstream in central Illinois may
limit max temps, but mid 30s appear likely and upper 30s to
locally 40 are possible where remaining snowpack is low/patchy
across northern Illinois.

Kluber


Tuesday Night through Sunday:

A robust shortwave will pass to our north Tuesday night,
eventually sending a modest cold front through the area. Ahead
of this, fairly strong DCVA and 60-80 m/12 hour height falls
will foster a decent amount of large scale forcing. At this
point, much of this will just go into saturating the mid and
upper levels, with a robust dry layer noted in regional
soundings below about 700 mb. That said, the combination of
strong ascent and slivers of steeper lapse rates in the 800-500
mb layer may support the development of high-based convective
elements within a narrow corridor ahead of the main vort max
Tuesday night. The latest ECMWF is now producing some light
precipitation south of I-80, although associated soundings still
look a bit marginal, with a substantial amount of dry air
present under 10 kft. Still not seeing quite enough support to
warrant a precip mention at this point, but continue to monitor
this period given the presence of a notable warm nose aloft
which could promote liquid precip falling onto still near to
sub-freezing ground.

Blustery northwest winds Wednesday morning in the wake of the
aforementioned cold front will quickly be replaced by
strengthening southerly flow Wednesday evening and overnight as
the next robust disturbance approaches and encourages a deep
surface low eastward across the Upper Great Lakes. Large scale
forcing with this system looks very impressive, with 12 hour 500
mb height falls pushing 200 meters. Ascent will rapidly
increase across the region very late Wednesday night which will
drive the development of widespread showers and drizzle towards
daybreak Thursday. While the NAM holds onto some near-freezing
temperatures across interior northern Illinois as precipitation
arrives, given the strong mass response in advance of this
system, suspect air temperatures and dewpoints will warm
sufficiently to preclude any frozen precipitation issues
Thursday morning.

A strong cold front will push through the area during the
afternoon Thursday. Associated cold advection will foster
increasing westerly wind gusts, particularly late in the
afternoon and into the evening hours. Gusts could near 40-45 mph
during this time as 10+ mb/6 hour pressure rises surge east of
the Mississippi River. Precipitation could potentially flip over
to a little snow before ending in the wake of the front, but
the window for this looks very brief before the mid and upper
levels rapidly dry out.

Temperatures look to fall quickly through the teens Thursday
night, and into the single digits across parts of northern
Illinois. Northwesterly breezes will linger into Friday morning
with wind chills falling near/below zero. If wind speeds stay up
a bit more than currently advertised (which remains possible),
wind chills could make a run towards 10-15 below for a brief
period early Friday morning across NW Illinois. Increased low-
level moisture overlapping much of the DGZ Thursday night may
result in the development of flurries at times. Depending on the
orientation of the boundary-layer flow, lake effect snow
showers could persist into early Friday morning over parts of
Porter County, but this remains a bit in question at this range,
with some guidance turning post-frontal winds more westerly
which would direct the LES potential into lower Michigan.

High pressure will only briefly build across the region on
Friday, and will be replaced by increasing southerly winds and
warm advection once again Friday night into Saturday. This
should allow temperatures to warm back into the 30s and 40s on
Saturday. Guidance now suggests that another cold front may send
temperatures back into the 20s and 30s on Sunday into Monday.

Carlaw

&&

.AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 1129 AM CST Mon Dec 15 2025

Concerns:
-Gusty SW winds to 25 kt, briefly to 30 kt MDW/ORD
-Fog development mainly W of MDW/ORD overnight

Gusty southwest winds will continue this afternoon before dropping
after 21-22z. Gusts are largely peaking at 25 kt with lighter
winds outside the urban terminals, and a few gusts to 30 kt
remain possible for a few more hours at ORD and MDW. Upper level
cloudiness will vary between BKN and SCT from time to time, and
with cloud breaks tonight there will likely be patches of fog
around as winds ease. The main window will be overnight and
west of ORD and MDW. Winds will be increasing out of the
southwest again fairly quickly on Tuesday. This should keep the
fog threat patchy, though where it forms it could be briefly
dense.

KMD


&&

.MARINE...
Issued at 254 AM CST Mon Dec 15 2025

A 50 knot low-level jet passing over southern Lake Michigan this
morning will lead to some southwesterly gale force gusts. A
very strong inversion below the the jet will limit the
frequency and magnitude of gales, with a possibility that gales
do not fully materialize before the low-level jet shifts
southeast this afternoon. Have maintained the Gale Warning but
limited wording to gale force gusts in the forecast, with the
main gale potential focused in a 14-18Z window.

Kluber

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 4 PM CST this afternoon for the IL
     and IN nearshore waters.

&&

$$

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